Cartilage is a form of mesodermal tissue derived from the connective tissue, which is created by multi-potent, undifferentiated, mesenchymal precursor cells. A distinction is made between three types of cartilage, hyaline, elastic and fibrocartilage. Hyaline cartilage is by far the most common form of cartilage and is found in the joint surfaces, for example. Cartilage defects caused by wear or damage are a widespread medical problem. Due to the denseness of the cartilage of the body's conventional inflammation and repair system, it has only a low capacity for self-healing. This being the case, methods and techniques have been developed in the past, and in particular over the last few years, as a means of replacing chondral as well as osteochondral areas in the joint cartilage. For example, joint cartilage has been replaced by perios, perichondrium, allogenic and autologous osteochondral grafts, allogenic meniscuses or prostheses made from synthetic materials.
In situations involving autologous grafting of chondrocytes, chondrocytes taken from the patient are grown in cell culture and given back to the patient again. They may be given back in the form of various different types of transplants. Examples of these are injection solutions which are injected into the joint, matrices injected with cartilaginous cells and similar.
Patent specification WO 97/15655 , for example, describes artificial tissue comprising three-dimensional extra-cellular matrices and genetically manipulated cells, and the matrices are able to release immunosuppressive or cell-differentiating factors. These matrices preferably take the form of a polymer fleece, through which a cell suspension, which may be suspended in a fibrinogen solution, is distributed. Factors or components of the corresponding extra-cellular matrix which are necessary for the growth and/or differentiation process may also be added to the matrix. In order keep the cells in the matrix, the cell suspensions may be solidified by adding thrombin, thereby resulting in the finished graft.
Patent specification DE 44 31 598 describes a method of producing an implant of cell cultures, whereby three-dimensional support structures to which the cells are applied are firstly encapsulated and then perfused with a nutrient solution. Resorbable micro-bodies are incorporated in the support structures, which release factors influencing tissue formation as they are resorbed.
Patent specification DE 43 06 661 describes a three dimensional support structure, preferably made from a polymer fleece, in which the cells are incorporated. The support structure is then perfused with nutrient solution in order to promote cell growth and the formation of an extracellular matrix by the cells. In order to prevent the cells from migrating or draining out, the support structure is encapsulated with agarose.
Patent specification DE 101 39 783 also discloses the use of mesenchymal cells in synovial fluid. If desired, this composition can also be applied to a support, such as a fleece or a plastic, and used as a graft in this form. Otherwise, the suspension of cells in synovial fluid is injected as such into the relevant joint.
Alternatively, matrix structures are synthesized which do not actually contain any cells. For example, patent specification US 2003/0003153 describes stiffened matrix membranes containing one or more structure-forming proteins suitable for cell growth. Suitable proteins are collagen, for example. The resultant matrices in membrane form may be injected with cells or grafted as they are. In the latter case, it is assumed that cells from the body's own tissue will migrate into the matrix structure. It is done by means of a conventional Pridie puncture or micro-fracturing, for example. With these techniques, small punctures or fractures are made in the joint bone as far as the bone marrow. Blood flows through the punctures into the defect, as a result of which the defect is filled with a blood graft. The graft contains mesenchymal precursor cells, which, stimulated by appropriate impetuses, are able to form a cartilage-type replacement tissue, the so-called fibrocartilage. If a matrix material is placed over the Pridie puncture, the blood cells are able to migrate into this matrix material, where they then become established.
Patent specifications DE 199 57 388 and WO 2005/014027 use this effect and enhance it by incorporating growth and differentiating factors (DE 199 57 388) or chemokines (WO 2005/014027) in the matrix structure as recruiting means. All the factors are intended to result in enhanced recruitment of cartilage-forming mesenchymal precursor cells, the ultimate aim being to regenerate the cartilage more rapidly.
Patent specification WO 02/00272 , finally, discloses the possibility of producing appropriate grafts from blood and a polymer component. The underlying problem addressed by this document is the fact that the blood graft which forms as standard using the Pridie puncture technique contracts on coagulation and thus changes shape. The added polymer prevents this change of shape and thus permits healing true to shape. In order to produce the graft, a polymer is mixed with blood or a blood component such as erythrocytes, leukocytes, monocytes, platelets, fibrinogen, thrombin and platelet-rich plasma and introduced into the defect. If using a blood component, however, the presence of material capable of coagulating is a significant factor in terms of achieving the desired effect.
Grafts made from chitosan and chondrocytes may be used as an alternative. Since the cells are introduced into the defect as described above, the addition of substances for attraction purposes and/or growth and differentiating factors can be dispensed with.
The technologies described above have disadvantages because if the graft itself contains cells, they are often damaged due to manipulation during handling, and if cells are used for the graft, in particular autologous cells, they have to be produced by a lengthy culture process and have to be carefully controlled to prevent contamination, and finally, there is no possibility of storage. In parallel, the recruitment of cell-free grafts of mesenchymal cells through a Pridie puncture, with or without substances used for attraction purposes, has proved unsatisfactory. Colonization is slow, is initiated by few cells and is also non-specific. This means that different cell types are flushed into the graft from the blood leaving the Pridie puncture and remain there. However, it is only colonization by mesenchymal precursor cells which differentiate to chondrocytes that is desired. In the case of conventional grafts, however, this is not guaranteed.
Amongst other things, therefore, the objective of the invention is to propose a graft which is simple to produce, can be readily stored and is simple to apply. Furthermore, it would be desirable to increase recruitment rates by means of the graft, obtain better selectivity for the type of cells recruited and disposed in the graft, and to dispense as far as possible with the use of growth factors foreign to the body and optionally even recombinant growth factors, which represent potential allergens.